Carrier balance and linear magnetoresistance in type-II Weyl semimetal WTe2

Unsaturated magnetoresistance （MR） has been reported in type-II Weyl semimetal WTe2, manifested as a perfect compensation of opposite carriers. We report linear MR （LMR） in WTe2 crystals, the onset of which was identified by constructing the MR mobility spectra for weak fields. The LMR further increased and became dominant for fields stronger than 20 T, while the parabolic MR gradually decayed. The LMR was also observed in high-pressure conditions.

Understanding the role of interconnecting layer on determining monolithic perovskite/organic tandem device carrier recombination properties

As one of the core parts of two-terminal(2 T) monolithic tandem photovoltaics, the interconnecting layers(ICLs) play a critical role in modulating the carrier transport and recombination between the sub-cells,and thus influencing the tandem device performance. Here, for the first time, the relationship between ICLs architecture and 2 T monolithic perovskite/organic tandem device performance has been studied by investigating the change of ICLs composition layer thickness on the ICLs optical and electrical properties, sub-cells EQE properties, and tandem device J-V properties. It is revealed that the ability of ICLs on modulating the sub-cells carrier balance properties is strongly associated with its composited layers thickness, and the tandem device carrier balance properties can be reflected by the relative EQE intensity between the sub-cells. Finally, with a deep understanding of the mechanisms, rational design of ICLs can be made to benefit the tandem device development. Based on the optimized ICL a high PCE of 20.03% is achieved.

Effect of net carriers at the interconnection layer in tandem organic solar cells

Tandem cell with structure of indium tin oxide(ITO)/molybdenum oxide(MoO_(3))/fullerene(C60)/copper phthalocyanine(CuPc)/C60/tris-8-hydroxy-quinolinato aluminum(Alq_(3))/Al was fabricated to study the effect of net carriers at the interconnection layer. The open circuit voltage and short circuit current were found to be 1.15 V and 0.56 mA/cm^(2),respectively. Almost the same performance(1.05 V, 0.58 mA/cm^(2)) of tandem cell with additional recombination layer(ITO/MoO_(3)/C60/Alq_(3)/Al/Ag/MoO_(3)/CuPc/C60/Alq_(3)/Al) demonstrates that the carrier balance is more crucial than carrier recombination. The net holes at the interconnection layer caused by more carrier generation from the back cell on one hand would enhance the recombination with electrons from the front cell and on the other hand would quench the excitons produced in CuPc of the back cell.

SWN: An SDN Based Framework for Carrier Grade WiFi Networks

With the rapid growth of mobile data traffic and vast traffic offloaded from cellular network, Wi-Fi has been considered as an essential component to cope with the tremendous growth of mobile data traffic. Although operators have deployed a lot of carrier grade Wi-Fi networks, but there are still a multitude of arrears for nowadays Wi-Fi networks, such as supporting seamless handover between APs, automatic network access and unified authentication, etc. In this paper, we propose an SDN based carrier grade Wi-Fi network framework, namely SWN. The key conceptual contribution of SWN is a principled refactoring of Wi-Fi networks into control and data planes. The control plane has a centralized global view of the whole network, can perceive the underlying network state by network situation awareness(NAS) technique, and bundles the perceived information and network management operations into northbound Application Programming Interface(API) for upper applications. In the data plane, we construct software access point(SAP) to abstract the connection between user equipment(UE) and access point(AP). Network operators can design network applications by utilizing these APIs and the SAP abstraction to configure and manage the whole network, which makes carrier grade Wi-Fi networks more flexible, user-friendly, and scalable.

Linker aggregation engineering of TADF materials to tune carrierbalance for highly efficient organic LEDs with long operationallifetime

Thermally activated delayedfluorescence(TADF)molecules are regarded as promis-ing materials for realizing high-performance organic light-emitting diodes(OLEDs).The connecting groups between donor(D)and acceptor(A)units in D–A type TADF molecules could affect the charge transfer and luminescence performance of TADF materials in aggregated states.In this work,we design and synthesize four TADF molecules using planar and twisted linkers to connect the aza-azulene donor(D)and triazine acceptor(A).Compared with planar linkers,the twisted ones(Az-NP-T and Az-NN-T)can enhance A–A aggregation interaction between adjacent molecules to balance hole and electron density.As a result,highly efficient and stable deep-red top-emission OLEDs with a high electroluminescence efficiency of 57.3%and an impressive long operational lifetime(LT_(95)∼30,000 h,initial luminance of 1000 cd m^(-2))are obtained.This study provides a new strategy for designing more effi-cient and stable electroluminescent devices through linker aggregation engineering in donor–acceptor molecules.

Realizing External Quantum Efficiency over 25% with Low Efficiency Roll-Off in Polymer-Based Light-Emitting Diodes Synergistically Utilizing Intramolecular Sensitization and Bipolar Thermally Activated Delayed Fluorescence Monomer

Since polymer-based light-emitting diodes(PLEDs)arewellsuited building blocks for large-area and low-cost flexible display equipment,state-of-the-art thermally activated delayed fluorescence(TADF)PLEDs are in high demand.To respond to this demand,light-emitting TADF units have initially been modified with electron-transporting units to balance the carrier transport of regiorandom TADF polymers,and simultaneously,an intramolecular sensitizing strategy has also been employed by covalently incorporating TADF sensitizers with light-emitting TADF units and hosts in conjugated polymers to accelerate the spin-flip of triplet excitons.Superior photophysical properties have been achieved by a rational regulation of the proportions of each component,achieving a photoluminescence quantumyield of 90%,an extremely high rate of reverse intersystem crossing of 3×106 s−1,and a relatively low nonradiative decay rate of around 105 s−1.As a result,the solutionprocessed PLEDs can attain an external quantum efficiency(EQE)value of 25.4%with emission peaks of around 550 nm,representing record-high performance for PLEDs.The efficiency roll-off can also be significantly suppressed,maintaining an EQE value of 24.2%at 1000 cd/m2 with ideal efficiency roll-off of lower than 5%.Encouragingly,this work provides a valid strategy to tackle the imperative need for PLEDs with high EQE and low efficiency roll-off.

Highly efficient green organic light-emitting devices based on terbium complex by employing hole block material as host

In this work,efficient green electroluminescent（EL）devices with simplified device structure were prepared by doping trivalent terbium complex Tb（PMIP）3into hole block material Tm Py PB.The high triplet energy of Tm Py PB helps to confine excitons within light-emitting layer,while the electron transport characteristic of Tm Py PB facilitates the balance of carriers on Tb（PMIP）a3molecules.By optimizing the doping concentration of Tb（PMIP）a3and the thickness of each functional layer,highly efficient green EL device with the structure of ITO/Mo Oa3（3 nm）/TAPC（50 nm）/Tb（PMIP）a3（30 wt%）：Tm Py PB（25 nm）/Tm Py PB（60 nm）/Li F（1 nm）/Al（100 nm）displayed pure Tb^3＋ characteristic emission with maximum current efficiency,power efficiency and brightness up to 47.24 cd/A（external quantum efficiency（EQE）of 14.4%）,43.63 lm/W and 1694 cd/m^2,respectively.At certain brightness of 100 cd/m^2,the device still maintained a current efficiency of 19.96 cd/A（EQE=6.1%）.Such a device design strategy helps to improve the EL performances of Tb（PMIP）a3and to simplify device fabrication processes,thus reduce the fabrication cost.

Efficiency enhancement of P3HT:PCBM polymer solar cells using oligomers DH4T as the third component

We assembled a ternary blend bulk heterojunction polymer solar cell(PSCs) containing P3HT(donor) and PC61BM(acceptor) incorporated with a small molecule oligomer, dihexyl-quaterthiophene(DH4T) as a third component. By optimizing the contents of DH4 T, we increased the power conversion efficiency of ternary P3HT:DH4T:PC61BM PSCs to 4.17% from 3.44% of binary P3HT:PC61BM PSCs under AM 1.5 G of 100 m W/cm2 intensity. The major improvement is from the increase of the short circuit current and fill factor that is due to the increased light absorption at short wavelength, the balanced charge carrier transportation and the enhanced hole evacuation by a DH4T-enriched layer at the anode interface. In this work, we demonstrated that the efficiency of the PSCs can be enhanced by using low-bandgap conjugated polymer and its oligomer as donors and fullerene derivatives as acceptors.